Adsorption isotherms, kinetics and thermodynamic studies of methylene blue dye removal using Raphia taedigera seed activated carbon

Abstract

This present work revealed the isotherm, kinetic, and thermodynamic behaviour of methylene blue (MB) dye adsorbed onto acidic activated carbon (AAC) and base activated carbon (BAC) prepared from Raphia taedigera seed by carbonization and chemical activation. AAC and BAC were activated with sulphuric acid and sodium hydroxide respectively. Batch equilibrium studies were done under different experimental conditions such as MB dye concentration and temperature. The equilibrium data were modelled using Langmuir, Freundlich, Elovich, Temkin and Dubinin-Radushkevich isotherms. The Langmuir isotherm model best describes the uptake of MB dye onto AAC and BAC with R2 > 0.998 in all cases. The pseudo-first-order, pseudo-second-order and intra-particle diffusion equations were used to evaluate the kinetic properties. It was observed that the adsorption of MB dye onto the two activated carbons could best be described by the pseudo-second order equation with 0.999 < R2 ≤ 1. Thermodynamic parameters such as Gibbs free energy (ΔG0), standard enthalpy (ΔH0), standard entropy (ΔS0), and activation energy (Ea) were determined. The results of ΔG0indicated a spontaneous and feasible for AAC and non-spontaneous but feasible for BAC. Results of ΔH0 confirmed that the adsorption of MB onto AAC and BAC are endothermic and physical in nature. It can be concluded that AAC and BAC prepared from Raphia taedigera seed could be used as low-cost adsorbent for the removal of MB dye from the wastewater.